A mechanical, valve-based device to modulate endotracheal tube cuff pressure reduces airway injury: an animal study.

Alexander J. Osborn MD PhD1, Rose Chami MD2, Paolo Campisi MD1, Evan Propst MD1, Igor Luginbuehl MD3, Glenn Taylor MD2, Joseph A. Fisher MD4, Vito Forte MD1Departments of (1) Otolaryngology, (2) Pathology, and (3) Anesthesia, University of Toronto, The Hospital for Sick Children, 555 University Ave, Toronto ON M5G 1X8, and (4) Department of Anesthesia, University of Toronto, The Toronto General Hospital, 200 Elizabeth St, Toronto ON M5G 2C4Abstract

Objective: To develop a reliable, inexpensive means of modulating endotracheal tube (ETT) cuff pressure in order to reduce airway injury related to endotracheal intubation.Setting: Animal laboratory in a tertiary care pediatric hospital.Subjects and Methods: 12 S. scrofa domesticus piglets (14-16kg) were intubated with standard endotracheal tubes and maintained in a hypoxic state to accelerate airway injury. Animals in the control group (n=6) were ventilated with a constant pressure of 20 cm H2O in the endotracheal tube cuff. Animals in the experimental group (n=6) were ventilated using a custom-designed circuit that altered the pressure in the endotracheal tube cuff with the ventilatory cycle. Larynges were harvested at the end of the experiment and examined histologically to determine the degree of airway injury induced by intubation.Results: Animals in the control group suffered significantly more airway damage than those animals that were ventilated using modulated endotracheal tube cuff pressure (mean damage score 1.6 vs 0.8, respectively). The differences were seen primarily in the subglottis, where the endotracheal tube cuff exerted the most pressure.Conclusions: We have designed a simple, reliable, and inexpensive means of modulating endotracheal tube cuff pressure with the ventilatory cycle. This modulation of endotracheal tubecuff pressure leads to a substantial decrease in airway injury in our animal model and has implications for the reduction of intubation-related injury in human patients.

The Device

To ventilator To patient

5 cm H2O PEEP valve

To ETT cuff

Figure 1. A mechanical valve-based device to modulate ETT cuff pressure. (a) A PEEP valve is placed in line with the ventilator circuit, and a connector joins the ventilator circuit with the ETT cuff. (b) On inspiration, gas flows to the patient and through the connector into the ETT cuff, inflating it (shown in cross section). The cuff pressure is 5 cm H2O higher than the airway pressure, ensuring that there is no leak. (c) On expiration, the pressure in the cuff is relieved. Thus, there is not sustained cuff pressure on the airway mucosa.

a.

Inspiration

b.

Expiration

c.

Figure 2. ETT cuff pressure is higher than airway pressure. Pressure tracings taken over 5 ventilatory cycles from regions proximal and distal to the PEEP valve are shown. Because of the gradient created by the PEEP valve, the cuff pressure is higher than the airway pressure, preventing a leak during positive pressure ventilation.

Injury Grading System0 Normal mucosa

1 Compression of the epithelium

2 Destruction or erosion of the epithelium

3 Inflammation to the level of the submucosal glands

4 Inflammation to the level of the perichondrium

Normal mucosa Grade 1 Grade 2

Grade 3 Grade 4 Grade 4(perichondrial detail)

Figure 3. An objective injury classification scheme is used. Pigs are kept intubated under hypoxic conditions to accelerate injury. Larynges are harvested and sectioned. Histologic examination is performed to determine the degree of laryngeal and tracheal injury caused by the ETT cuff. Representative sections are shown.

0

2

4

6

8

10

12

14

Supraglottis Subglottis

Airway dam

age (aggregate)

Control

Modulated

Glottis Trachea

P<0.01

Parameter Control ModulatedBody Weight (kg) 15.4 16.1 NSTemperature (C) 37.0 37.2 NSPulse (bpm) 131 134 NSSystolic Blood Pressure (mm Hg)

61 66 NSDiastolic Blood Pressure (mm Hg)

36 39 NSO2 Saturation (%) 69.7 68.5 P<0.05PaCO2 39.6 44.2 P<0.05pH 7.43 7.41 NSTidal Volume (cc) 166 184 P<0.05Respiratory Rate 20 22 P<0.05

Table 1. Physiologic parameters of animals intubated with eitherconstant cuff pressure (control) or modulated cuff pressure. Parameters that are significantly different are indicated as such, while those that did not differ between the groups are indicated as not significant (NS). The mild increase in ventilatory dead space introduced by the device resulted in slightly higher PaCO2 levels, larger tidal volumes, and faster rates in the animals ventilated with modulated cuff pressure.

Figure 4. Modulated cuff pressure results in significantly less airway injury. Each larynx was sectioned and assessed for grades of injury. Scores from multiple sections were aggregated into a composite score for each subsite. Degree of injury was significantly less in those animals intubated with modulated cuff pressure.

Conclusions

We have developed an inexpensive and reliable means of modulating endotracheal tube cuff pressure

This pressure modulation reduced endotracheal injury in our hypoxic porcine model